Hubble Space TelescopeObservations of the Large Magellanic Cloud Field around SN 1987A: Distance Determination with Red Clump and Tip of the Red Giant Branch Stars

Abstract

We have used Hubble Space Telescope (HST) WFPC2 multiband observations of a field around SN 1987A in the Large Magellanic Cloud to measure its distance from the Sun. The observations allowed us to carefully determine the interstellar extinction along the line of sight to a large number of stars and to measure the LMC distance by using two stellar distance indicators: the red clump (RC) and the tip of the red giant branch (TRGB). From an application of the red clump method, we obtain a distance modulus of (m - M) = 18.59 ± 0.04 ± 0.08 mag (statistical plus systematic error), in good agreement with the distance derived by using the TRGB stars, namely, (m - M) = 18.69 ± 0.25 ± 0.06 mag (statistical plus systematic error). Both values agree well with the distance to SN 1987A as determined from a study of its inner ring fluorescent echo [(m - M)SN 1987A = 18.55 ± 0.05 mag], thus excluding distance moduli lower than 18.43 to a 99.7% significance level. Differences with respect to previous results obtained using the same distance indicators are discussed.